A small watercraft such as a canoe equipped with an outboard motor is disclosed in U.S. Pat. No. 3,918,666, for example. This craft is a canoe to which an outboard motor is detachably mounted to provide propulsive power.
An auxiliary buoyant unit with floats provided to a small watercraft for adding buoyancy to the small watercraft is disclosed in U.S. Pat. No. 3,294,055, for example. This small watercraft has a structure in which the floats (auxiliary buoyant bodies) are extended to the right and left of a hull to which a propulsion unit is fixedly provided, and the right and left floats are attached to opposite ends of an arm pivotally mounted to the hull. The auxiliary buoyant bodies provided to the small watercraft are fixedly attached to the hull, and the maneuverability of the hull as a whole is fixed. Therefore, it is impossible to choose between maneuvering of the hull without the propulsion unit and maneuvering of the hull with the propulsion unit.
A very small watercraft for play or sport such as a surfboard is not usually provided with a propulsion unit, and is manipulated by riding on the crest of wave in a standing position utilizing an elemental force (force of a wave). A surfboard fixedly provided with a propulsion unit is disclosed in Japanese Utility Model Laid-Open Publication No. HEI-1-95499, for example. This surfboard is configured to be propelled by a jet-pump-type screw or impeller provided in a rear portion of the surfboard and driven by an engine horizontally provided in the surfboard.
With this art, however, since the engine and the screw are provided in the plate-shaped surfboard, the surfboard as a whole is increased in size and weight. The surfboard is thus only used as a craft propelled by a propulsion machine, and cannot be used for the sport of surfing, a watercraft sport with agility for which a surfboard is intended. The surfboard with the propulsion unit is very expensive for a surfboard.
Another surfboard fixedly provided with a jet-pump-type propulsion unit is disclosed in Japanese Patent Laid-Open Publication No. HEI-4-71989, for example.
This jet-pump-type surfboard includes a nozzle of a jet pump fixedly provided at the rear of the surfboard, which is a laterally movable steering nozzle. The nozzle is rotated for steering by operating a hydraulic cylinder. In this art, a plumb bob detects a positional change of the surfboard; a switching valve is operated by a pilot pressure from a pilot valve; and the hydraulic cylinder is operated utilizing the water pressure of a jet pump slipstream to rotate the steering nozzle, thereby to steer the surfboard.
However, since this surfboard also has the propulsion unit integrally provided in the board, the board as a whole is increased in size and weight. The surfboard is thus only used as a watercraft propelled by the propulsion unit, and cannot be used for the sport of surfing, a watercraft sport with agility for which a surfboard is intended. In addition, this surfboard is also a surfboard with a propulsion unit, and is very expensive for a surfboard.
The above-described small watercraft to which the outboard motor is detachably mounted, disclosed in U.S. Pat. No. 3,918,666 is a canoe steered in a seated position, to which the outboard motor is detachably mounted. A canoe is rowed manually with a paddle. In the art disclosed in this patent, however, the outboard motor is detachably mounted to the rear of the canoe which is propelled by the outboard motor when necessary. The outboard motor is swung right and left by a steering bar for manual steering. That is, the canoe has great buoyancy, and is steered by turning operation of the outboard motor.
The above-described surfboards disclosed in Japanese Utility Model Laid-Open Publication No. HEI-1-95499 and Japanese Patent Laid-Open Publication No. HEI-4-71989 each include the propulsion unit provided in the board. The surfboard of HEI-1-95499 does not include a steering means. The surfboard disclosed in HEI-4-71989 includes the steering nozzle of the integral propulsion unit, which is rotated to change the direction of jets. The canoe of U.S. Pat. No. 3,918,666 is, in short, steered in a similar manner as an outboard motor.
That is, if an operator operates the surfboard with the propulsion unit mounted, by hand-operating the steering bar from a predetermined position, the operator is occupied by a steering feel as felt in a conventional outboard motor. As a result, dynamic pleasure produced from riding the flat-bottomed surfboard of short or little draft dies away.
For this reason, demand exists for an art which allows an operator or rider, when steer-controlling the direction of propulsion by a propulsion unit, to turn the propulsion unit in line with tilting actions by waves of a hull, by shifting his weight sideways, keeping a balance between buoyancy and gravity, to steering the hull, without hand-operating a steering bar.